Polyolefin films, and, in particular, polypropylene films, have become a dominant factor in the packaging film industry in recent years, thanks to a spectrum of favorable properties. However, the realization of the full potential of these films as packaging materials has been hampered by their lack of good resistance to the transmission of oxygen.
A very desirable approach to improving the oxygen and also the moisture vapor transmission rate of polypropylene films is the application of a metal, usually aluminum, coating to one or both surfaces of the film. Many journal articles and patents have been published relating to the application of metal barrier coatings and metal coating is widely practiced in the film industry at the present time. Metal coating is, however, a relatively costly technique as it involves extra surface preparation steps and costly application apparatus and processes.
It is also known to prepare films and containers of polypropylene using composite structures comprised of polypropylene layered with another material having better oxygen transmission properties, e.g. polyvinyl or polyvinylidene chloride, vinyl acrylate/acrylonitrile copolymer or a vinyl alcohol polymer or copolymer. Further, it is known to prepare films having good oxygen transmission properties in which small, discrete particles of polypropylene are dispersed throughout a vinyl alcohol polymer matrix.